1. Field of the Invention
The present invention relates to a technique which synthesizes a video and a still image.
2. Background and Prior Art
In television interests or the like, an image synthesizing process which displays telop characters on a video photographed by a video camera or a video reproduced by a video player is popularly performed. In image synthesis, an apparatus such as a switcher is used. FIG. 1 is a typical view showing image synthesis performed by a switcher 1. The switcher device 1 receives a background video 2 and a telop video 3 to be synthesized and synthesizes these videos. More specifically, the switcher device 1 receives a video signal corresponding to the background video 2 through a video cable 4 for transmitting a video signal. The switcher device 1 receives a video signal corresponding to the telop video 3 through a video cable 5 for transmitting a video signal. The switcher 1 synthesizes the two received video signals according to an operation instruction based on an operation of a user or a control instruction from an external device (not shown) to generate a synthesis video signal and to output the synthesis video signal. FIG. 1 shows a video 7 expressed by the synthesis video signal.
When images are to be synthesized by a switcher, a technique called Chromakey is mainly used. The outline of the Chromakey technique is as follows. A video signal for the background image 2 is input, and a video signal expressing a character having a blue background is input as the telop image 3. An image obtained by extracting a part except for a blue part of the telop image 3 from the background image 2 and an image obtained by extracting a blue part from the telop image 3 are synthesized to obtain a synthesis image 7. In image synthesis using a Chromakey technique, when the telop image 3 is input to the switcher 1, the video signal of an image having the same size as that of a screen is frequently transmitted as a component signal or the like of an analog format.
However, in the above method, a still image (telop character or the like) is displayed on only a lower part of the screen, the still image 3 having the same size as that of the entire screen is necessary. For this reason, an amount of signal (data amount of the still image 3) flowing in the video cable (transmission path) 5 increases and is wasted.
In addition, the data amount of the still image 3 increases, a memory capacity spent by one image increases. Therefore, in order to store and display a large number of images, a memory having a large capacity is necessary, and the cost of the apparatus becomes high. In addition, when the position of telop characters to be displayed is changed, the image data of the image must be changed and transmitted again, and therefore operation efficiency becomes poor.